Date (Phoenix dactylifera L.) palm stones as a potential new feedstock for liquid bio-fuels production

Fuel 210 (2017) 165–176

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Full Length Article

Date (Phoenix dactylifera L.) palm stones as a potential new feedstock for liquid bio-fuels production

MARK

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Abdelrahman B. Fadhila, , Mohammed A. Alhayalia, Liqaa I. Saeedb a b

Laboratory Researches of Industrial Chemistry, Department of Chemistry, College of Science, Mosul University, Mosul, Iraq Chemistry Department, College of Education for Girls, Mosul University, Mosul, Iraq

A R T I C L E I N F O

A B S T R A C T

Keywords: Date (Phoenix dactylifera L.) palm stones Date stones oil Biodiesel evaluation and analysis Pyrolysis Bio-oil Analysis of bio-oil

In the present investigation, Date (Phoenix dactylifera L.) stones were utilized in the production of different types of biodiesel in addition to bio-oil. The oil was extracted from the date stones with a yield of 10.50 wt% and is used in the production of fatty acid methyl, ethyl and mixed methyl/ethyl esters via KOH- catalyzed transesterification process with methanol, ethanol and mixed methanol and ethanol, respectively. Properties of the obtained biodiesels, such as the density, kinematic viscosity, flash point, acid value, cloud and pour points, total and free glycerin contents and the refractive index were evaluated and found comparable to those of ASTM D 6751 biodiesel. The FTIR spectroscopy confirmed conversion of date stone oil to biodiesel. The date stones were also tested as new non-edible feedstock for bio-oil production by pyrolysis process in a semi batch reactor. The influence of the pyrolysis temperature, pyrolysis time and precursor particles size on the bio- oil yield was investigated. Maximum bio- oil yield (52.67% ± 1.50) was obtained at 500 °C pyrolysis temperature with a pyrolysis time of 60 min and feed particle size of 0.25 mm. The ultimate analysis, FTIR spectroscopy and adsorption column chromatography were determined to characterize the chemical composition of the obtained biooil. Furthermore, several important fuel properties, like the density, kinematic viscosity, flash point, pour point and the acidity index of date stones bio- oil were also determined following ASTM standard test methods and found comparable to those documented for other bio- oils in literature. The chemical composition of the bio- oil produced through pyrolysis of date stones showed the potential of date stones as an important source of alternative fuel and chemicals as well.

1. Introduction The increasing emissions rates of greenhouse gases have become a threat to the world climate due to the continuous use of fossil based fuels. Accordingly, development of economical and energy-efficient processes have become an urgent need. Biomass as a source of energy has received more attention because it represents part of the alternative solution for the replacement of fossil fuels. The use of biomass as a source of energy will reduce emissions of greenhouse gases and also reduces reliance on fossil based fuels [1–4]. Many processes were used for the conversion of biomass into fuels, such as pyrolysis, gasification, combustion, hydrogenation and liquefaction. Transesterification is a thermo-chemical process which aims to convert triglycerides into a successful alternative to petro diesel, namely biodiesel. It includes the reaction of triglycerides with an alcohol in the presence of a suitable catalyst, like a base, an acid or an enzyme [5]. Many non-edible feedstock oils were used in the production of biodiesel, such as Croton megalocarpus [6], Prunus dulcis [7,8],

⁎

Corresponding author. E-mail address: [email protected] (A.B. Fadhil).

http://dx.doi.org/10.1016/j.fuel.2017.08.059 Received 4 June 2017; Received in revised form 30 July 2017; Accepted 13 August 2017 Available online 31 August 2017 0016-2361/ © 2017 Elsevier Ltd. All rights reserved.

Prunus sibirica [9], Rhazya stricta Decne [10], rubber seed oil [11], Silybum marianum L [12,13] and wild Brassica Juncea L. [14]. Pyrolysis is another thermochemical process. It has gained a special concern due to it can directly produce various products from biomass, like solid, liquid and gases through thermal decomposition in absence of oxygen [4,15]. Bio-oil or pyrolytic oil is the liquid product obtained via pyrolysis of biomass. It is a dark-brown organic liquid composed of a complex mixture of oxygenated hydrocarbons, and water is the main liquid fuel that can be obtained via pyrolysis of biomass. It can be used as a liquid fuel after being upgraded or it can be blended with diesel fuel. Besides, it is source of synthetic chemical feedstocks [15–17]. Different biomass wastes were used in the production of bio- oil via the pyrolysis process. Among biomass wastes, de-oiled seed cakes which are the solid residue leftover after the oil extraction from vegetable seeds via pressing or solvent extraction were utilized for this purpose. Pyrolysis of black cumin seed cake in a fixed -bed reactor was investigated by Sen and Kar who found that 450 °C was the optimal pyrolysis temperature due to it gave the highest bio-oil yield [3].

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physico-chemical properties of the obtained bio-oil were also determined as per the ASTM standard test methods. Different techniques were used for analyzing the resulting bio-oil, such as elemental analysis, Fourier Transform Infra-Red Spectroscopy and the adsorption column chromatography.

Aldobouni et al. [5] conducted pyrolysis of de-oiled castor seed cake in a semi-batch fixed bed reactor and found that maximum bio-oil yield was obtained at a pyrolysis temperature of 450 °C. Biradar et al. [17] have produced bio-oil from de-oiled Jatropha curcas seed cake in a fluidized -bed pyrolysis system and found that an operating temperature of 450 °C has given the best yield of bio-oil. Bio-oil production by pyrolysis of de-oiled rapeseed cake in a fixed- bed reactor was conducted by Ucar and Ozkan who obtained maximum bio-oil yield at 500 °C pyrolysis temperature [18]. However, pyrolysis of some agroseeds to produce bio- oil were also documented in the literature. Kader et al. [19] investigated pyrolysis of tamarind seed in a fixed-bed firetube heating pyrolysis system. Pyrolysis of karanja seed for the production of bio- oil in a semi batch reactor at different temperatures was reported by Shadangi and Mohanty [2]. Ucar and Karago studied pyrolysis of pomegranate seeds using a semi-batch fixed bed reactor [20]. Sal seeds were pyrolyzed in a semi-batch reactor at a temperature range of 400–625 °C and at a heating rate of 20 °C min−1 [21]. Duman et al. [22] investigated the production of bio- oil from cherry seed by pyrolysis in a fixed-bed and fluidized bed reactors at different pyrolysis temperatures. Pyrolysis of Niger seed in a semi batch reactor with and without the presence of a catalyst was reported by Shadangi and Mohanty [23]. Neem seeds were also used as a feedstock for bio-oil production by the pyrolysis in a semi-batch reactor at a temperature range of 400–500 °C at a heating rate of 20 °C min−1 [1]. Castor seeds were pyrolyzed in a semi batch reactor at different temperatures 400–600 °C to produce bio-fuel [15]. Pradhan et al. [24] reported pyrolysis of Mahua seed using a semi-batch reactor at various temperatures from 450 to 600 °C under constant flow rate of nitrogen 30 mL min−1 and constant heating rate 20 °C min−1. Pyrolysis of safflower seed in a fixed-bed lab-scale reactor to produce bio-oil was also studied by Onay [25]. Finally, pyrolysis of cottonseed to produce liquid bio-fuel was also documented in the literature [26]. Iraq is one of the largest world producers of dates with more than 21 million date-palm trees and an annual production of about 566,828 tons of the fruit. It was reported that the average weight of a date stones is about 10–15% of the date fruit weight[27,28]. The use of the date stones as a source of energy was investigated by several authors. Al-Omari [28] investigated the combustion of date stones in a small scale furnace with a conical solid fuel bed and the results indicated that date stones can be considered as a promising renewable source of energy. The use of date stones as a fuel in furnaces was also tested by Al-Omari [29] who found that the date stones contain many volatile materials that are released during the pyrolysis process, and hence it can be used as a source for energy. The use of date stones for biodiesel production has been reported in the literature by Azeem et al. [30], Jamil et al. [31] and Amani et al. [32]. However, all those works related to the production of fatty acid methyl esters but not fatty acid ethyl esters or mixed fatty acid methyl ethyl esters. Moreover, the production of bio- oil from date stones via pyrolysis was only reported by Albadri and Lafta [33] who investigated the pyrolysis of date stones under N2 atmosphere at 400 °C, and did not investigate the effect of the pyrolysis conditions, such as temperature, time, and other parameter on the bio- oil yield. Nevertheless, the production of bio- oil through pyrolysis of date stones has not yet been reported in detail in the literature. The production and evaluation of biodiesels and bio-oil from date (Phoenix dactylifera L.) stones was the main target of the present investigation. Oil from the date stones was extracted and its properties and fatty acid profile were determined. The date stones oil was utilized in the preparation of different types of biodiesel, namely fatty acid methyl esters, fatty acid ethyl esters and mixed fatty acid methyl ethyl esters through base-catalyzed transesterification. The resulting biodiesels were characterized for their fuel properties following ASTM standard test methods. The conversion of date stones oil into biodiesel was confirmed by FTIR spectroscopy. Bio-oil has also produced from date (Phoenix dactylifera L.) stones via the optimized pyrolysis process. The

2. Materials and methods 2.1. Materials The date fruit (about 10 kg) used in the present study for biodiesel and bio-oil production were obtained from the local markets located in the city of Mosul, North of Iraq during the summer of 2013. Various analytical reagent grade chemicals of different origins were utilized, such as potassium hydroxide (KOH, 99%, BDH), petroleum ether (60–80 °C, BDH), methanol (99%, Fluka), Absolute ethanol (99.90%, BDH), Hydrochloric acid (36.50%, Fluka), sodium carbonate (99%, BDH), n-hexane (BDH), sodium sulfate (Na2SO4, BDH) and dimethyl ether (BDH). All chemical reagents and solvents were provided at analytical grade and purer. 2.2. Preparation of date stones Fig. 1 shows steps followed to prepare biodiesel and bio-oil from date (Phoenix dactylifera L.) seeds. Before utilization of the date (Phoenix dactylifera L.) seeds as a feedstock for producing biodiesel and bio-oil, the seeds were immersed in boiling water with vigorous agitation for 5 h to remove dust and the residue of the dates. Afterward, the stones were left to settle so as to separate the floated seeds which can be easily separated by decanting. The cleaned stones were dried at 50 °C for about 24 h and kept for further use. 2.3. Oil extraction from date stones The date (Phoenix dactylifera L.) dried seeds were milled in a heavyduty grinder in order to pass 40 mesh screen. The oil extraction process was carried out in a Soxhlet apparatus for 10 h with petroleum ether solvent (60–80 °C). After the filtration to remove the solid particles and impurities, the oil was separated from the solvent by a rotary evaporator. The physical and chemical properties of date stone oil (DSO) were determined according to ASTM standard test methods. Hanus method was followed to determine the iodine value of the DSO [34]. The fatty acid composition of DSO was determined by GC/MS analysis [35]. The functional groups present in the DSO were identified by Fourier Transform Infra-Red spectroscopy using a Bruker Alpha FTIR Spectrometer, USA Fourier transformed infrared spectrophotometer with a resolution of 4 cm−1, in the range of 400–4000 cm−1. 2.4. Synthesis and properties evaluation of biodiesel from DSO The DSO (approximately 100 g) was fed to the reactor (three-neck round bottom flask attached to a reflux condenser and a thermometer). A pre-established amount of KOH was dissolved in alcohol (methanol, ethanol or mixed methanol and ethanol) at a molar ratio of 6:1 alcohol to oil. The reaction took place for 60 min at specified reaction temperature under reflux while the mixture was being stirred. At the end, the reaction products (alkyl ester and glycerin) were separated in a separating funnel according to the difference in their density. The alkyl ester layer was stripped of excess alcohol by the rotary evaporator, followed by washing with warm water. The washed alkyl ester was then dried by passing over sodium sulfate [5,13]. The ester content on the purified biodiesel was determined based on Bindhu et al. [36] method. One gram of the biodiesel was diluted in n-hexane and loaded onto a silica gel (60–120 mesh) packed in an adsorption glass column (18 × 46 cm). Later, 300 mL of a mixture of hexane: diethyl ether 99.5:0.5% v/v was utilized for eluting the alkyl ethyl ester fraction. The 166

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Fig. 1. Liquid biofuels preparation steps.

Palm date stones

Crushing to powder form

Oil Extraction

Pyrolysis

Transesterification with alcohol and KOH

Pyrolytic oil

Bio-char Characterization and analysis Biodiesel

Glycerin

Purification

Characterization and analysis

refractive index (D1747 – 09) following ASTM standard test methods. The Cetane number (CN) of all the biodiesel samples was calculated based on the saponification value (SV) and the iodine value (IV) of the samples using the following formula [37]:

solvent system was then stripped from the alkyl ester fraction, which was calculated on a weight basis. The biodiesel yield was calculated as follows [5,13]:

BD yield(%) =

Weight of the fatty acid alkyl esters X Ester content(%) Total weight of oil used(g)

CN = 46.3 +

× 100

5458 −0.225 X IV SV

The higher heating value (HHV) of fatty acid alkyl esters was calculated following equation given by Krisnangkura [37]:

Several interesting properties which are very important to assess biodiesel as a fuel for diesel engines were determined, including the density at 15.5 °C (ASTM D5002), kinematic viscosity at 40 °C (ASTM D445), flash point (ASTM D93), cloud and pour points (ASTM D 2500), acid value (ASTM D664), saponification value (ASTM D5555-95), and

HHV = 49.43−[0.041(SV ) + 0.015(IV )] AOCS Cc 17-95 was followed to determine the soap content in the prepared biodiesels [38], while Pisarello et al. [39] method was applied 167

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chemical properties of the obtained bio- oil, including density at 15.5 °C and 40 °C, kinematic viscosity at 40 °C, the flash and pour points, the refractive index at 20 °C and acid value were determined as per ASTM standard test methods. The HHV of date stones bio- oil was also determined based on the ultimate analysis [3]. The pH of the bio-oil was also determined using the pH meter HANNA instruments, PH 211, microprocessor. The Fourier Transform Infra- Red (FTIR) spectroscopy of the bio- oil and its sub-fractions was conducted using a Fourier transformed infrared spectrophotometer (Bruker Alpha FTIR Spectrometer, USA) with a resolution of 4 cm−1, in the range of 400–4000 cm−1 using Nujol mull as reference so as to characterize various functional groups found in the obtained bio- oil. The chemical composition of the obtained biooil was determined by liquid column chromatography fraction. The biooil was first separated into n-hexane soluble fraction which is known as maltenes and hexane insoluble fraction which is known as asphaltenes. The n-hexane soluble fraction was further separated by adsorption chromatography. The chromatography column was packed with activated silica gel 70–230 mesh. The column was then eluted successively with n-hexane, toluene and methanol to produce aliphatic fraction, aromatic fraction and polar fraction (resin), respectively [4,3].

to determine the free and total glycerin contents in the biodiesels. Each property was measured in triplicate and the results were presented as the mean ± standard deviation (SD). The FTIR spectroscopy was utilized to confirm the conversion of DSO to fatty acid alkyl esters and to detect various functional groups existing in the obtained biodiesel. The spectra was measured using a Fourier transformed infrared spectrophotometer (Bruker Alpha FTIR Spectrometer, USA) with a resolution of 4 cm−1, in the range of 400–4000 cm−1 using Nujol mull as reference. 2.5. Production of bio-oil from date stones 2.5.1. Analysis of date stones The elemental analysis of the date stones was performed on a Perkin 240 C Elemental Analyzer to determine the carbon, hydrogen and nitrogen contents, while the oxygen content was calculated by difference. Thermogravimetric analysis (TGA) of the raw date stones was performed using a METTLER TOLEDO TGA/DCS Thermal Analyzer in pottery (silica) crucibles at temperatures ranging from 25 to 600 °C with a heating rate of 20 °C/min under air atmosphere. A horizontal balance was used in order to scanning TGA. The proximate analysis of date stones was also determined as per ASTM standards. Contents of moisture, volatile matter, ash, and fixed carbon were determined based on ASTM D3172-07a method. Higher heating value (HHV) of date stones was determined according to Dulong’s formula et al. [3]. The chemical composition of the date stones including extractives, cellulose, hemicellulose and lignin contents was determined following procedures described by the national renewable energy laboratory (NREL) [40].

3. Results and discussions 3.1. Properties of DSO and its biodiesels The maximum oil yield obtained from date stones by solvent extraction is 10.5% w/w on dry basis which lies within the range of oil content reported for date stones (5.7–12.7% w/w) [42]. Moreover, it is comparable to that published for okra seed (12 wt%) [43], but is less than the oil content of other non-edible oil seeds, like Yucca aloifolia seeds (16.23 wt%) [44] Rhazya stricta Decne seeds (13.86 wt%) [10], Jatropha curcas seeds (55–60 wt%) [45], Ceiba pentandra seeds (25–28 wt%) [45], Silybum marianum L seeds (28.0 wt%) [12,13] and apricot seed kernels (48.88 wt%) [46] .Thus, DSO can be a promising source of oil for biodiesel production. As a result, the DSO was investigated thoroughly to estimate whether its properties are conformed to ASTM standard and suitable for biodiesel production as shown in Table 1. The density of DSO was comparable to that of kapok oil (0.9232 g/mL) [47], but is lower than that observed for tung oil (0.9410 g/mL) [48]. The DSO has lower kinematic viscosity value than Silybum marianum L seed oil (42–45.20 mm2/s) [12,13], kapok oil (31.20 mm2/s) [47], tung oil (102.70 mm2/s) [40], Jatropha curcas seed oil (35.40 mm2/s) [45] and Ceiba pentandra seed oil (29.32 mm2/s) [45]. It was noticed that the flash point of DSO was comparable to those reported for other non-edible oils, such as Jatropha curcas seed oil (186 °C) [45] and apricot seed kernel oil (186 °C) [46], but lower than the flash point of Silybum marianum L seed oil (230 °C) [12,13]. It's well known that the iodine value and pour point of an oil relates greatly to its fatty acids composition, in particular unsaturated fatty acids. On this account, it was found that the DSO has lower iodine value (47.66 100 mg I2/g) than Jatropha curcas seed oil (101.0 100 mg I2/g) [45], Ceiba pentandra seed oil (101.90 100 mg I2/g) [45], Silybum marianum L seed oil (99.0 100 mg I2/g) [12,13] and apricot seed kernel oil (101.32 100 mg I2/g) [46]. On the other hand, the DSO has higher cloud and pour points than Silybum marianum L seed oil [12,13] and apricot seed kernel oil [46]. The DSO has lower acid value (1.23 mg KOH/g) than other non-edible oils, such as Silybum marianum L seed oil (13.60–20 mg KOH/g) [12,13], okra seed oil (3.40 mg KOH/g) [43], Yucca aloifolia oil (10.99 mg KOH/g) [44], Jatropha curcas seed oil (11.0 mg KOH/g) [45] and Ceiba pentandra seed oil (28.71 mg KOH/g) [45]. As a result, direct base-catalyzed transesterification is suitable to produce BD from DSO. Table 1 also displays the fatty acid composition of DSO in comparison to other vegetable oils [32,45]. As shown in Table 1, the unsaturated fatty acid level of DSO (51.45%) is higher than its saturated

2.5.2. Pyrolysis of date stones A laboratory scale fixed bed reactor heated by an electric furnace was used to carry out the pyrolysis experiments. The reactor is made of stainless steel with 10 cm internal diameter and 25 cm height. A thermocouple immersed inside the reactor was utilized to control temperature. The pyrolysis experiments were performed under atmospheric pressure and under a flow of N2 gas for removal of air from the reactor and all the gases produced during pyrolysis. The pyrolysis experiments were conducted using 40 g of the feedstock which was placed in the reactor and heated from room temperature to the final pyrolysis temperature for specific pyrolysis time. The resulting vapors and gases passed through a trapping system which consisting of a spiral condenser cooled with the circulation of icy water so as to decrease the temperature to below 0 °C. Liquids condensed in the a spiral condenser were collected in conical flasks fitted to the condensers and immersed in a cooling bath consisting of an ice, acetone and salt [4]. The resulting liquid fraction (bio-oil) was separated into two phases, aqueous (bottom phase) and organic rich compounds (upper phase). The bio-oil yield was calculated as follows [41]:

Bio−oil yield(%) =

Weight of bio−oil produced × 100 Weight of feedstck used

The bio-char leftover after the pyrolysis of the feedstock was collected and its yield was calculated as follows [41]:

Bio−char yield(%) =

Weight of bio−char produced × 100 Weight of feedstck used

The gaseous product yield was calculated as follows [41]:

Gases yield(%) = 100−[% liquid + % char] 2.5.3. Analysis of bio- oil The bio- oil produced through pyrolysis of date stones was analyzed for its ultimate analysis using a Perkin 240C Elemental Analyzer which provides carbon, hydrogen and nitrogen, while the oxygen content was calculated from the difference. When the sum of these components is subtracted from 100, it gives oxygen percentage. The physical and 168

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Table 1 Properties and fatty acid composition of DSO in comparison to other non-edible oils. Property

DSO

CCPOa

CJCOa

SMSOb

ASKOc

Oil content (% w/w) Density @ 15.6 °C Kinematic Viscosity @ 40 °C Flash Point, °C Acid Value, mg KOH/g oil Saponification Value, mg KOH/g oil Iodine Value, g I2/100 mg Refractive index @ 20 °C Cloud Point, °C Pour Point, °C Cetane Number HHV

10.50 ± 1.50 0.9211 ± 0.0012 27.8 2 ± 0.58 186 ± 1.0 1.23 ± 0.05 212 ± 2.0 47.66 ± 1.50 1.4611 ± 0.0002 6.0 ± 0.50 3.0 ± 0.50 61.32 40.02

25–28 0.9210 29.32 – 28.71 195.0 101.90 – – – 51.36 39.92

60–55 0.9180 35.40 186.0 11.0 – 101.0 – – – – –

28.0 0.9141 42–45.20 230 13.6–20 195.0 99 1.4700 −2 −8 52.01 39.96

48.88 0.9124 26.65 186 0.68 187.22 101.32 1.4688 −4.0 −8.0 – –

Fatty acid composition

DSO#

CCPOa

CJCOa

Soybean oild

Rapeseed oild

Palm oild

C12 C14 C16 C18 C18:1 C18:2 C18:3 Others Total saturated FA Total unsaturated FA Total polyunsaturated FA Total monounsaturated FA

11.36 11.44 13.84 6.56 51.45 0.0 0.0 5.35 43.20 51.45 0.0 51.45

0.11 – 23.2 5.68 29.69 35.11 – 4.07 30.88 65.05 35.11 29.69

0.10 – 14.20 7.0 44.70 32.80 0.20 0.30 21.3 78.4 33.0 45.40

0.0 0.0 10.58 4.67 22.52 52.34 8.19 1.70 15.25 83.05 60.53 22.52

0.0 0.0 3.49 0.85 64.40 22.30 8.23 0.0 4.34 86.78 22.38 64.40

0.0 0.6–2.40 32–46 4–6.30 37–53 6–12 0.0 0.0 – – – –

a

From Ref. [35]. From Ref. [45]. c From Ref. [12]. d From Ref. [46]. # From Ref. [32]. b

Table 2 Properties of biodiesels from DSO. Property

FAME

FAEE

Mixed FAMEE

Rapeseed FAMEd

Palm oil FAMEd

Yield (%) Density @ 15.6 °C (g/mL) Kinematic Viscosity @ 40 °C (mm2/s) Flash Point, °C Acid Value, mg KOH/g Saponification Value, mg KOH/g Iodine Value, g I2/100 Cloud Point, °C Pour Point, °C Refractive Index @ 20 °C Cetane number HHV Total glycerol, wt% Free glycerol, wt%

95.88 ± 1.5 0.8781 ± 0.0012 3.91 ± 0.25 141 ± 1.5 0.10 ± 0.02 224 ± 1.0 48.51 ± 2.0 3.0 ± 0.50 −1.0 ± 0.50 1.4544 ± 0.0001 59.75 39.52 0.11 ± 0.01 0.015 ± 0.001

92.77 ± 2.0 0.8811 ± 0.00110 4.31 ± 0.22 147 ± 1.0 0.14 ± 0.020 221 ± 1.50 48 ± 1.50 4.0 ± 0.50 1.0 ± 0.50 1.4561 ± 0.0002 60.19 39.65 0.13 ± 0.02 0.015 ± 0.002

96.62 ± 1.5 0.8788 ± 0.0010 3.98 ± 0.21 145 ± 1.0 0.11 ± 0.01 0 ± 1.5223 48 ± 2.0 3.0 ± 0.50 −1.0 ± 0.50 1.4548 ± 0.0001 59.97 39.57 0.12 ± 0.01 0.01 ± 0.002

– 0.8820 4.83 155 – – 94.0 −4.0 −10.80

– 0.8800 5.70 164 – 201.0 57.0 13.0 – – 60.0 40.33 – –

52.90 – – –

FAME = Fatty acid methyl esters produced using 1.0 wt% KOH; 6:1 methanol: oil molar ratio; 60 °C; 60 min. FAEE = Fatty acid ethyl esters produced using 1.0 wt% KOH; 6:1 ethanol: molar ratio; 70 °C; 60 min. FAMEE = Fatty acid methyl/ethyl esters produced using 1.0 wt% KOH;6:1 mixed methanol/ethanol molar ratio; 65 °C; 60 min. d From Ref. [32].

fact that the reactivity of methanol toward transesterification reaction is faster than that with ethanol. In comparison to mixed methanol/ ethanol system, the presence of methanol in the alcoholic system makes transesterification process to proceed faster than that with ethanol alone due to methanol is more reactive than ethanol. Moreover, the presence of methanol in the alcohols mixture will make separation of glycerin from the reaction products easier and faster. As such, transesterification with methanol or mixed alcoholic system gave higher BD yield than with ethanol. Another possible reason is that the applied conditions could be suitable for alcoholysis reaction using methanol or mixed ethanol/methanol system and not with ethanol. Table 2 lists the fuel properties of the obtained biodiesels in comparison to ASTM D6721 BD. It can be seen from this table that the

fatty acid content (43.20%) [35]. Moreover, monounsaturated fatty acid content of DSO was much lower than those of other non-edible oils [32,45]. The low content of polyunsaturated fatty acids in an oil results in lower deterioration of its oxidation stability. Nevertheless, the DSO has higher saturated fatty acid content than other non-edible oils. This finding reflects the lower iodine value and higher pour point, Cetane number and HHV of DSO than other non-edible oils. The DSO was used in the synthesis of different types of biodiesel (fatty acid methyl esters, fatty acid ethyl esters and mixed fatty acid methyl/ethyl esters) through KOH-catalyzed transesterification with methanol, ethanol and mixed methanol and ethanol system. The highest yield was obtained for the mixed fatty acid methyl/ethyl esters whereas the fatty acid ethyl esters exhibited the lowest yield due to the 169

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DSO

Biodiesel

Fig. 2. The FTIR spectra obtained for DSO and its biodiesel.

88.61% and 91.86%. Moreover, the acid values of the produced biodiesels were lower than those published for biodiesels produced from Okra seed oil (0.39 mg KOH/g) [43], kapok seed oil (0.57 mg KOH/g) [51] and Milo (Thespesia populnea L.) seed oil (0.25 mg KOH/g) [52]. The pour point of biodiesels produced from DSO is lower than that established for okra seed oil biodiesel (2 °C) [43] and kapok oil biodiesel (4 °C) [51]. The free glycerin and total glycerin contents of the prepared biodiesels were much lower than the standard limits which indicate the high purity level of the obtained fuels. It is also obvious from Table1 that fuel properties of fatty acid methyl esters and mixed fatty acid methyl/ethyl esters were better than those of the fatty acid ethyl esters. These findings belong to the higher ester content of the fatty acid methyl esters and mixed fatty acid methyl/ethyl esters than the ethylic biodiesel. Nonetheless, properties of the biodiesels from DSO were within the standards limits specified by the ASTM standards. The FTIR spectra can be used to characterize many of the key functional groups which are related to the BD content. Moreover, the difference in the chemical structure between the oil and biodiesel can

density of the produced fuels ranged from 0.8781 to 0.8811 g/mL, which are comparable to those published for biodiesels produced from other non-edible oils, such as bitter almond oil (0.8702 g/mL) [8], Silybum marianum L. seed oil (0.8780 g/mL) [13], wild mustard (Brassica juncea L.) seed oil (0.8760 g/mL) [14], rapeseed oil (0.8820 g/mL) [32], palm oil (0.8800 g/mL) [32] and waste fish oil (0.8798 g/mL) [49]. The kinematic viscosity values of the resulting biodiesels were between 3.91 and 4.31 mm2/s. The obtained values were also comparable to those documented for biodiesels produced from other nonedible oils, such as bitter almond oil (4.53 mm2/s) [8], Silybum marianum L. seed oil (4.50 mm2/s) [13], wild mustard Brassica juncea L. seed oil (3.33 mm2/s) [14], rapeseed oil (4.83 mm2/s) [32] and palm oil (5.70 mm2/s) [32]. The flash point values of the resulting biodiesels ranged from 141 to 174 °C. The obtained values are lower than those observed for biodiesel from bitter almond oil biodiesel (165 °C) [8], rapeseed oil (155 °C) [32], palm oil (164 °C) [32], waste fish oil (160 °C) [49] and biodiesel produced from waste chicken fat (174 °C) [50]. The reduction in the acid value of the DSO ranged between 170

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biodiesels in the literature[5].

Table 3 Analysis and chemical composition of date stones in comparison to other seeds and shells. Ultimate analysis

C% H% N% O% HHV

Date stones

48.43 6.44 0.670 42.20 24.25

Proximate analysis Moisture% 5.44 ± 1.0 Ash% 1.47 ± 0.22 Volatiles% 79.88 ± 2.50 18.65 ± 1.50 Fixed carbon % Component analysis (dry, wt%) Cellulose 43.88 ± 2.0 Hemi 17.67 ± 1.0 cellulose Lignin 16.33 ± 0.55 Extractives 8.2 ± 0.50 1 2 3 4 5

From From From From From

Ref. Ref. Ref. Ref. Ref.

pistachio shell1

Peach stones2

Apricot kernel shells3

Cherry stones4

3.2. Characterization of date stones

Mahua seed5

42.41 5.64 0.070 51.87 22.21

45.92 6.09 0.580 47.38 24.07

47.33 6.37 0.370 45.93 24.29

52.48 7.58 4.54 35.30 24.11

61.24 8.40 4.12 25.50 25.30

6.99 0.09 80.01 12.08

9.3 1.10 71.70 17.90

0.38 0.95 75 15.75

5.35 1.16 77.72 15.69

8.60 2.0 84 5.4

53.98 20.10

46 14

29.57 17.01

32.06 28.59

32.4 7.9

25.25 0.67

33 7

47.97 –

29.08 8.70

29 31

The ultimate and proximate analysis of the date stones are presented in Table 3. It was found that the date stones have higher carbon and hydrogen contents than pistachio shells [53], peach stones [54] and apricot kernel shells [55]. In contrast, date stones have lower oxygen content than other biomass wastes [53–55]. As shown in Table 3, the HHV of the date stones was higher than that of pistachio shell [53] and comparable to those of other biomass wastes [22,24,54]. The proximate analysis of the date stones revealed that its moisture content is much lower than that of pistachio shell [53], peach stones [54] and apricot kernel shells [55]. Nayan et al. [1] has reported that the high moisture content in biomass affects its heating value and its conversion efficiency as well as increases its decomposition tendency, leading to energy loss during storage. The volatile matter evolves in the form of tars, light hydrocarbon and gases [1,15]. It was documented that biomass with higher volatile matter is more readily devolatized than solid fuel [4,15]. The volatile matter of date stones was higher than those reported for pistachio shell [53], peach stones [54], apricot kernel shells [55] and cherry stones [22]. The ash content of date stones was comparable to that reported for other biomass wastes [22,24,53–55]. The literature has documented that the ash content of biomass depends upon the plant and soil condition in which the plant grows [4,15]. Table 3 also lists the relative concentration of lignin, cellulose and hemicellulose of the date stones in comparison to other shells and stones [22,24,53–55]. The lignin content of the date stones was lower than that of other biomass wastes [22,24,53–55]. Casoni et al. [56] have stated that the lower amount of lignin in biomass would lead to a less complex bio- oil. Fig. 3 shows thermal gravimetric analysis (TGA) thermograph of the date stones at heating rate of 20 °C min−1 under air atmosphere. The TGA thermograph shows the characteristic parameters of de-volatilization of date stones. As seen from Fig. 3, the TGA of date stones has shown that the initial slight mass loss between 45 and 160 °C could be attributed to the evaporation of moisture and some volatile compounds from the date stones. The first stage of pyrolysis could be attributed to the fast pyrolysis of the date stones which was observed in the range of 165–240 °C. This stage indicates the beginning of cellulose and hemi cellulose decomposition. The second decomposition stage in the region between 240 and 375 °C was attributed to the decomposition of hemicellulose. The third zone was in the range of 350–450 °C and could be ascribed to the decomposition of both cellulose and lignin. However, above 500 °C, no significant decomposition was observed. The TGA

[53]. [54]. [55]. [22]. [24].

be distinguished through FTIR spectrum in particular in the range of 1500–900 cm−1. Fig. 2 shows the FTIR spectra of the DSO and its fatty acid methyl esters. As seen from Fig. 2, the peak which relates to asymmetric stretching of (–CH3) is observed at 1436 cm−1. This peak is found in biodiesel and absence in the parent oil. The presence of (O–CH3) group (mono-,di-,triglyceride) was assigned at 1376 cm-1. The absorption peaks in the range of 2800–3000 and 1653–1740 cm−1 indicate the (–CH3) stretching vibration (–CO–O–CH3) and the stretching of carbonyl group (–C]O), respectively [49,50]. The FTIR spectroscopy can also be used to confirm the conversion of triglycerides into corresponding alkyl esters. This was concluded through comparing area under the absorption peaks of the stretching C]O band, C–H stretching band and the C–H bending band of the alkyl esters which are much lower than their corresponding in the original oil. Moreover, the broad absorption peak at 3439 cm−1 which attributed to the hydroxyl group of fatty acid has disappeared in the obtained biodiesel [49,50]. The observed functional groups were similar to those reported for other

Fig. 3. TGA thermo-gram of Palm (Phoenix dactylifera L.) date stones.

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Bio-oil

55

Fig. 4. Effect of pyrolysis temperature on the products yield.

Bio-char

50

Gases and loss

Yield, %

45 Particel size=0.84 mm Time= 60 minutes

40 35 30 25 20

350

400

450

500

550

600

650

55

Fig. 5. Effect of pyrolysis time on the products yield.

Bio-oil

50

Bio-char

45

Gases & loss

Yield, %

40

Particle size= 0.84 mm Temperature= 500°C

35 30 25 20 15 10

30

80

130

180

Time, minutes 60

Bio-oil

Fig. 6. Effect of particles size of the precursor on the products yield.

Bio-char

50

Gas and Loss

%, Yield

40

Temperature=500°C Time= 60 minutes

30 20 10 0 0.25

0.45

0.65

0.85

1.05

1.25

Paticle size, mm

temperature between 400 and 652 °C exhibited maximum bio-oil yield (52.8%) at the pyrolysis temperature of 600 °C [10]. In the study conducted by Demiral and Kul [55], the apricot kernel shells were pyrolyzed in a fixed- bed reactor at various temperatures 300–600 °C and the highest yield of bio- oil was obtained at 500 °C. Pyrolysis of pistachio shells at different temperatures was investigated by Acıkalın et al. [53] who obtained maximum yield of bio- oil (52.73%) at a pyrolysis temperature of 500 °C. Singh and Shadangi [5] investigated the pyrolysis of castor seed in a fixed- bed reactor at various temperatures (450–600 °C) and reported the highest bio-oil yield at 550 °C. Pyrolysis of tamarind seed was conducted in fixed-bed fire-tube reactor at temperatures ranged from 350 to 550 °C, and the highest liquid yield was 45% at 400 °C pyrolysis temperature [19]. Maximum yield of biooil from safflower seeds (54%) was obtained at a pyrolysis temperature of 600 °C [25], while a yield of 57% was obtained by thermal pyrolysis

thermograph of date stones was similar to that presented by Sait et al. [57]. However, as the TGA of date stones was conducted under air atmosphere, the decomposition stages cannot only be attributed to pyrolysis stages, but also to combustion.

3.3. Influence of pyrolysis temperature on products yield The date stones were pyrolyzed with a heating rate of 10 °C min−1 in relation to the final pyrolysis temperatures of 350, 400, 450, 500, 550 and 600 °C under nitrogen atmosphere. As shown in Fig. 4, the products yield was greatly affected by raising the pyrolysis temperature such that the bio- oil yield increases with increasing the pyrolysis temperature. The bio- oil yield increased from (41.2% ± 2.5) at 350 °C and reached maximum (50.10% ± 2.0) at a pyrolysis temperature of 500 °C. The pyrolysis of Sal seeds in a reactor-furnace system at the 172

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Table 4 Properties and composition of bio-oil obtained from date stones via pyrolysis. Sample Pyrolytic Pyrolytic Pyrolytic Pyrolytic Pyrolytic

oil oil oil oil oil

from from from from from

date stones pistachio shells1 apricot shells3 Mahua seeds5 pomegranate seeds6

Property

[email protected] °C Specific [email protected] °C Kinematic viscosity @40 °C (mm2/s) Flash point °C Pour point °C Acid value mg KOH/g pH Refractive index @20 °C HHV MJ/kg

C%

H%

N%

O%

HHV MJ/kg

73.56 67.44 64.45 69.23 64.26

10.50 7.82 8.24 9.12 8.21

1.26 0.42 018. 2.53 2.06

14.68 24.32 26.50 18.14 25.43

37.38 – 27.19 39.02 34.76

Date stones pyrolytic oil

Karanja seed pyrolytic oil7

tamarind seed pyrolytic oil8

Castor seed pyrolytic oil9

Diesel fuel

0.9572 ± 0.0012 0.9580 ± 0.0012 13.50 ± 0.22 87.0 ± 0.50 2.0 ± 0.50 85.0 ± 1.50 3.3 ± 0.50 1.4871 ± 0.0021 37.38

0.9384 0.9300 27.90 40 16 – – – 33.9

– 1.15 6.51 9 8–4 – – – 25

0.9660

0.8300 0.8307 2.04 77 −16 – – 1.4780 45–42

Fuels

81.19 31 < 5.0 – 3.7 – –

Fractionation of date stones bio-oil Sample

Date stones pyrolytic oil Rapeseed pyrolytic oil10

Fractions

Sub-fractions

Asphaltenes (wt%)

Maltenes (wt%)

Saturates (wt%)

Aromatics (wt%)

Resins (wt%)

15.56 ± 1.25 13

84.44 ± 1.20 87

31 ± 1.0 35

29.3 ± 1.50 37

40.7 ± 1.0 28

6

From Ref. [20]. From Ref. [41]. 8 From Ref. [19]. 9 From Ref. [15]. 10 From Ref. [18]. 7

pyrolysis time. Nevertheless, pyrolysis time over 60 min resulted in continuous decrease in the bio- oil yield. These findings were in consistence with those observed during pyrolysis of de-oiled castor seed cake [4] and pistachio shells [53]. On the other hand, the gaseous products yield increased proportionally with increasing the pyrolysis time, whereas the bio-char yield decreased. This phenomenon could be attributed to the secondary reactions of the pyrolysis vapors, resulting in the formation of lower molecular weight non-condensable gaseous products [5,10]. Similar results were also documented by Alobouni et al. [4], Acıkalın et al. [53] and Fadhil et al. [58] upon pyrolysis of deoiled castor seed cake, and pistachio shells and de-oiled fish waste, respectively. Therefore, 60 min were established as the optimal time for pyrolysis.

of karanja seed at a temperature of 500 °C using a semi batch reactor [41]. Finally, production of bio- oil from Mahua seed (Madhuca indica) was conducted by Pradhan et al. [24] in a semi-batch reactor at temperatures between 450 and 600 °C who found that maximum bio-oil yield was obtained at a pyrolysis temperature of 525 °C. Nevertheless, variation in the optimal amount of bio- oil produced from various feedstocks could be attributed to many factors, such chemical composition of the feedstocks used in the production of the bio- oil and the operation conditions applied on pyrolysis, like heating rate and sweeping gas flow rate. Fig. 4 also shows that temperatures higher than 500 °C reduced the liquid yield. This could be attributed to that secondary cracking reactions of the pyrolysis oil into non-condensable gases are associated with relatively higher pyrolysis temperatures. As a result, the bio-oil yield decreased [1,2,4,11,15,23]. It is obvious from Fig. 4, the bio-char yield decreased from (37% ± 1.5) to (22% ± 1.0) with the increment of pyrolysis temperature, which may be due to the greater primary decomposition of the date stones or secondary decomposition of the char residues with raising the temperature. On the contrary, the gaseous product yield increased with increasing the pyrolysis temperature. This could be ascribed to secondary cracking of the pyrolysis vapors or the formation of some non-condensable gaseous products during secondary decomposition of the char at higher temperatures. Similar results were also reported by several investigators [1,2,4,11,15,24,25]. Therefore, 500 °C was chosen as the optimal pyrolysis temperature.

3.5. Influence of particles size on products yield The particle size has an influence on the heat and mass transfer rates as well as the extent of secondary reactions inside the particles. Type of biomass and type of the pyrolysis process could determine the useful particle size of the raw feedstock [59]. Pyrolysis of the date stones was conducted using different feed particles size (0.25, 0.40, 0.59, 0.841 and 1.19 mm) as shown in Fig. 6. As expected, maximum bio-oil yield was produced using the smallest particles size feed. This finding could be ascribed to that smaller particles size feeds are favorable in the fast pyrolysis system may be due to the fact that the smaller particles sizes will heat up uniformly, resulting in the release of more volatile matter with more bio-oil and gas product yields. Aldobouni et al. [4], Onay et al. [24], Fadhil et al. [58], Hu et al. [60] have also published similar achievements upon the pyrolysis of castor de-oiled seed cake, safflower seed, de-oiled fish waste and blue-green algae blooms and, respectively. However, a significant decrease in the bio-oil and gases yields were observed with increasing the feed particle size. In contrast, the bio-char yield increases. This achievement suggested that mass- and heat-

3.4. Influence of pyrolysis time on products yield The pyrolysis of date stones in a fixed- bed reactor was conducted at different time intervals ranged from 30 to 150 min by 30 min increment under nitrogen gas atmosphere as shown in Fig. 5. The results revealed that the bio- oil yield has increased from 44.22% ± 2.50 after 30 min of pyrolysis and reached maximum (50.10% ± 2.0) at 60 min 173

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BO

Polar fraction

Aromatic fraction

Saturates fraction

Fig. 7. The FTIR spectra obtained for bio-oil and its sub-fractions.

engines or furnaces [4,62]. The calorific value of the bio- oil was 37.38 MJ kg−1, which is higher than that reported for the bio- oils produced form other seeds, such as karanja seeds [41] and tamarind seeds [19], and closer to that of diesel fuel. It was found that the resulting bio- oil has higher density and viscosity values than those of the diesel fuel. However, blending of the bio-oil with different transportation fuels could reduce its high density and viscosity. In contrast, the density and viscosity values of the obtained bio- oil were lower than those reported for bio- oils produced from karanja seeds [41] and castor seeds [15], but higher than those of the bio- oil produced from tamarind seeds [19]. The flash point of the bio- oil obtained from the pyrolysis of the date stones was higher than that of diesel fuel and thus will ensure safe storage. Besides, the flash point of the obtained bio- oil was higher than those of karanja seeds [41], castor seeds [15] and tamarind seeds

transfer restrictions had a profound influence when larger particles size feed is used, resulting in minimum bio-oil and gases yields. Moreover, increasing the feed particles size results in greater temperature gradients inside the particle such that at a given reaction time the core temperature would be lower than that at the surface of the particle. This may give rise to an increase in the liquid and char yields and a decrease in the bio-oil and gas product yields [59,61]. 3.6. Analysis of date stones bio-oil The fuel properties of date stones bio- oil, such as the density at 15.5 °C, kinematic viscosity at 40 °C, flash point, pour point, refractive index and acid value were determined as per ASTM standards. These properties are important for the use of the bio- oil as a fuel in boilers, 174

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hand, the oxygen content in the produced bio- oil was much lower than that observed for other bio- oils from the literature [19,41], which is useful for the bio- oil to be used as a fuel.

[19] bio- oils. The refractive index at 20 °C of the bio- oil was closer to that observed for diesel fuel. The pour point of the prepared bio-oil was 2 °C. It is much higher than that reported for diesel fuel but lower than the pour points of karanja seeds [41], castor seeds [15]and tamarind seeds [19] bio- oils. It was noticed that the pH of the resulting bio- oil was comparable to that reported for castor seeds bio- oil [15]. The high values of density, viscosity, flash point, pour point and refractive index of the bio- oil produced from date stones in comparison to diesel fuel could be attributed to the higher molecular mass of bio- oil than that of diesel fuel [4,58]. On the other hand, variation in the values of the fuel properties of various fuels could be attributed to the variation in the chemical composition of the parent feedstock used in their production. Bio-oil is chemically composed of a complex mixture of different organic compounds. Therefore, the resulting bio-oil was simplified through fractionating it into different components using column chromatography technique. The bio-oil was treated with n-hexane to yield maltenes and asphaltenes as given in Table 4. The result thus indicated that the date stones bio-oil composes of 84.44% w/w and 15.56% w/w maltenes and asphaltenes, respectively. Besides, the maltenes yield was closer to that reported for safflower seed bio- oil (87%) [12]. The results also disclosed that the aliphatic, aromatic, and polar sub-fractions of the maltenes are 31%, 29.3% and 40.7%, respectively. In addition, the aliphatic subfraction yield was closer to that obtained from safflower seed bio- oil [12]. Nonetheless, it was found that the bio- oil was predominantly formed of oxygenated compounds. The FTIR spectrum of the bio-oil and its sub-fractions produced by the pyrolysis of the date stones is depicted in Fig. 7. These results showed that the obtained bio-oil is composed of several functional groups belonging to various families of organic groups, namely aliphatic groups, oxygenated functions and aromatic groups. The oxygenated functions family is characterized by the presence of different oxygen bearing groups such as that observed at 3447 cm−1 which corresponds to the (–OH) stretching vibration caused by alcohol structures, acid, water and phenols. The stretching band of the (C]O) group which belongs to the presence of carboxylic acid and esters groups was assigned at around 1742 cm−1. The absorption peak at 1160 cm−1 corresponds to the (C–O) stretching vibration in the fatty acids. The aliphatic groups family can be characterized by the intense peaks at 2921 cm−1 and 2852 cm−1. These absorption bands are assigned to the existence of methylene groups (CH2). The absorption peak at 1462 cm−1 is attributed to asymmetric deformation vibrations of methylene and methyl groups, while the absorption band observed at 1416 cm−1 corresponds to stretching vibration of the methyl group. The absorption peak above 721 cm−1 corresponds to the deformation vibrations by unbranched aliphatic chains with more than four CH2 groups. The presence of the absorption peak at 3006 cm−1 indicated the presence of aromatic groups family in the produced bio-oil due to this band is attributed to (C]CH) symmetric stretching vibration. The aromatic (C]C) stretching vibration was observed as a small absorption peak at 1564 cm−1, whereas that observed at 900 cm−1 corresponds to bending vibration of (C–H) functional groups associated with aromatic structures. It can also be seen from Fig. 7 that the FTIR spectra of the sub-fractions are similar but differ in the area under the absorption peak of some functional groups, such as those observed at 2921 cm−1 and 3009 cm−1, 3447 cm−1, 1674 and 1724 cm−1 and 722 and 1021.44 cm−1. Moreover, the absorption peaks at 3447 cm−1 was observed in the bio-oil, polar fraction and aromatic fraction, but is absent in the saturates fraction. Nevertheless, the FTIR spectra of the bio- oil and its subfractions were similar to those of some bio-oils reported in literature and their subfractions [4,10,17,48–52]. Table 4 lists the ultimate analysis of the date stones bio-oil which exhibited higher carbon and hydrogen contents than those documented for bio- oils produced from pomegranate seeds [20], Mahua seeds [24], pistachio shells [53] and apricot kernel shells [55]. Consequently, biooil from date stones is expected to have higher heating value than biooils produced from other shells and seeds [19,23,26,10]. On the other

4. Conclusions Date (Phoenix dactylifera L.) stones were utilized for producing different types of liquid bio-fuels, namely biodiesel and bio-oil. Oil from the date stones was extracted in a Soxhlet apparatus, and used in the production of fatty acid methyl esters, fatty acid ethyl esters and mixed fatty acid methyl/ethyl esters. The fuel properties of the resulting biodiesels were determined and found conformed to those prescribed by ASTM D 6751. Moreover, the FTIR spectra confirmed the conversion of date stone oil to biodiesel and was similar to those reported for other biodiesels in literature as well. The date (Phoenix dactylifera L.) stones were pyrolyzed in a semi-batch fixed bed reactor for producing pyrolytic oil (bio-oil) with a maximum yield of (52.67% ± 1.50) at a pyrolysis temperature of 500 °C, 60 min pyrolysis time and a feed of 0.25 mm particles size. The FTIR spectroscopy, ultimate analysis and adsorption column chromatography were utilized to determine the chemical composition of the resulting bio- oil. The ASTM standard test methods were followed to measure the fuel properties of date stones bio- oil which were comparable to those documented for other bio- oils in the literature. It was concluded that date stones bio- oil can be used as a potential feedstock for producing alternative fuels and chemicals as well. Acknowledgment The authors would like to express their sincere gratitude and thanks to Mosul University, College of Science, Chemistry Department for their assistance to conduct this research work. References [1] Nayan NN, Kumar S, Singh RK. Production of the liquid fuel by thermal pyrolysis of neem seed. Fuel 2013;103:437–43. [2] Akhtar J, Amin NS. A review on operating parameters for optimum liquid oil yield in biomass pyrolysis. Renew Sustain Energy Rev 2012;16:5101–9. [3] Sen N, Kar Y. Pyrolysis of black cumin seed cake in a fixed-bed reactor. Biomass Bioenergy 2011;3(5):4297–304. [4] Aldobouni IA, Fadhil AB, Saied IK. Conversion of de-oiled castor seed cake into biooil and carbon adsorbents. Energy Sources Part A 2015;37:2617–24. [5] Fadhil AB, Emaad TB, Al-Tikrity B, Albadree Muhammed A. Transesterification of a novel feedstock, Cyprinus carpio fish oil: influence of co-solvent and characterization of biodiesel. Fuel 2015;162:215–23. [6] Aliyu B, Agnew B, Douglas S. Croton megalocarpus (Musine) seeds as potential source of bio-diesel. Biomass Bioenergy 2010;34:1495–9. [7] Atapour M, Kariminia HR. Characterization and transesterification of Iranian bitter almond oil for biodiesel production. Appl Energy 2011;88:2377–81. [8] Fadhil AB, Aziz AM, Altamer MH. Potassium acetate supported on activated carbon for transesterification of new non-edible oil, bitter almond oil. Fuel 2016;170:130–40. [9] Wang LB, Yu HY. Biodiesel from Siberian apricot (Prunus sibirica L.) seed kernel oil. Bioresour Technol 2012;112:335–8. [10] Nehdi IA, Sbihi HM, Al-Resayes SI. Rhazya stricta Decne seed oil as an alternative, non-conventional feedstock for biodiesel production. Energy Convers Manage 2014;81:400–6. [11] Reshad AS, Tiwari P, Goud VV. Extraction of oil from rubber seeds for biodiesel application: optimization of parameters. Fuel 2015;150:636–44. [12] Fadhil AB, Aziz AM, Altamer MH. Biodiesel production from Silybum marianum L. seed oil with high FFA content using sulfonated carbon catalyst for esterification and base catalyst for transesterification. Energy Convers Manage 2016;108:255–65. [13] Fadhil AB, Ahmed KM, Dheyab MM. Silybum marianum L. seed oil a novel feedstock for biodiesel production. Arab J Chem 2017;10:S683–90. [14] Aldobouni IA, Fadhil AB, Saied IK. Optimized alkali - catalyzed transesterification of wild mustard (Brassica juncea L.) seed oil. Energy Sources Part A 2016;38(15):2319–25. [15] Singh RK, Shadangi KP. Liquid fuel from castor seeds by pyrolysis. Fuel 2011;90:2538–44. [16] Ben Hassen-Trabelsi A, Kraiem T, Naoui S, Belayouni H. Pyrolysis of waste animal fats in a fixed-bed reactor: production and characterization of bio-oil and bio-char. Waste Manage 2014;34:210–8. [17] Biradar CH, Subramanian KA, Dastidar MG. Production and fuel quality upgradation of pyrolytic bio-oil from Jatropha Curcas de-oiled seed cake. Fuel

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